The present invention relates to a manufacturing method for a liquid crystal display panel and an apparatus therefor and, more particularly, to a manufacturing method of a liquid crystal display panel which can suppress the occurrence of bubbles during the injection of a liquid crystal material into a cell gap, and facilitate the control of cell thickness, and an apparatus therefor.
Liquid crystal displays (hereinafter, referred to as LCDs) have the advantages of a low leakage current level in liquid crystal itself, no need for high storage capacities, and small power dissipation. As a result, the demand for LCDs is increasing. Of the LCDs, a twisted nematic (TN) type LCD and a super twisted nematic (STN) type LCD are the more common ones.
However, a polarizing plate is required on each surface of a panel for a conventional TN type or STN type LCD, and such polarizing plates deteriorate light transmissivity, leading to a decrease in the luminance of the LCD. Especially when a color filter is used, a strong light source is necessary, since the intensity of transmitted light is less than 10% of that of incident light, thereby resulting in the an increase in dissipation.
As a way to overcome the problems, a polymer dispersed liquid crystal display (PDLCD) adopting a light scattering mode wherein a polymer is dispersed into a liquid crystal, has been recently developed. The PDLCD applies the principle that when an electric field is not applied, incident light scatters due to a disparity in the refractive index of the liquid crystal and the polymer, while when an electric field is applied, the liquid crystal is arranged in the direction of the electric field, and thus the incident light is transmitted. As is noted, relying on the principle of light scattering and transmission, the PDLCD does not use polarizing plates, consequently obtaining excellent luminance since its light utilization efficiency is higher than that of a conventional LCD.
Such a PDLCD is generally manufactured by a phase-separation method utilizing the difference in the solubility of a polymer and a liquid crystal (see U.S. Pat. Nos. 4,688,900 and 4,685,771). That is, the manufacture of a PDLCD is accomplished by utilizing the principle that liquid crystal droplets are formed by dissolving the liquid crystal in the monomers of a transparent polymer resin (hereinafter, referred to as monomers) and thereafter, polymerizing the monomers or oligomers of the polymer resin by ultraviolet irradiation or heating.
There are a vacuum injection method and a compression method for the injection of a liquid crystal into a cell gap in a manufacturing process of a LCD panel. The vacuum injection method is currently employed for a TN type or STN type LCD, both of which being the most widely used LCDs, for the reason that it simplifies the manufacturing process and facilitates the control of cell thickness after injecting a liquid crystal.
The vacuum injection method will be described in detail. The injection of liquid crystal is generally accomplished by reducing the inside pressure of a cell gap between two substrates and submerging an injection port (formed on one of the two substrates) into a container filled with liquid crystal.
However, the above vacuum injection method has a problem. That is, optical properties may be deteriorated due to the occurrence of bubbles in the cell gap when injecting the liquid crystal material.
Especially, in the case of a PDLCD utilizing the principle of light scattering and transmission, the existence of bubbles in a cell gap greatly decreases a contrast ratio. Moreover, when injecting a liquid crystal material under high vacuum state, a high-volatile monomer contained in the material is evaporated, thus leading to the change of a compounding ratio, being an essential factor to determine optical properties, of the liquid crystal and the monomer.
Therefore, a compression method is used for injecting a liquid crystal in the fabrication of a large PDLCD panel. The compression method is advantageous to the fabrication of a large display device, but it exhibits the disadvantages of difficulty with the control of cell thickness, which is an important factor to determine optical properties, and excessive consumption of liquid crystal, thereby increasing fabrication cost. In addition, for the purpose of sealing the edge, which is necessary after injecting the liquid crystal material in order to prevent the leakage of the liquid crystal material, a portion for binding should be cleaned to improve the adhesiveness of a substrate and an adhesive, thus making the manufacturing process complicated.